a. Field of the Invention
This invention relates to the field of networked computing. More specifically, the invention relates to the clustering of computers to support a set of remote services.
b. Related Art
An Encapsulated Cluster (EC) is characterized by a Connection-Router (CR) node and multiple server hosts providing a set of services (e.g. Web service, NFS, etc.). An example of a system which provides encapsulated clustering is described in U.S. Pat. No. 5,371,852, entitledxe2x80x9cMETHOD AND APPARATUS FOR MAKING A CLUSTER OF COMPUTERS APPEAR AS A SINGLE HOST ON A COMPUTER NETWORKxe2x80x9d.
Remote clients request services from the EC using protocols based, for example, on TCP/IP (e.g. HTTP). The service time for each request varies depending on the type of service, and the availability of the corresponding server applications. Hence, a naive allocation of connections quickly creates a skewed allocation that under utilizes the available EC resources, and introduces unnecessary delay to the requests.
The prior art has shown that there are many performance problems relating to scaling servers. See, for example, NCSA""s World Wide Web Server: Design and Performance, IEEE Computer, Volume 28, Number 11, November 1995, Pages 68-74. Consider an EC which uses round-robin DNS to support Web servers (i.e. httpd demons). The servers provide access services to video streams, database queries, and static web pages via http. The service time for each type of request varies widely depending on the type of services being provided, and the actual content involved. For instance, a complex database query could take orders of magnitude more time than providing a static, pre-loaded HTML page. This imbalance in request processing time often causes skewed utilization of the server cluster. Related problems with round-robin DNS are described in User Access Paterns to NCSA""s Worldwide Web Server, Kwa et al, Technical Report UIUCDSD-R-95-1394, Department of Computer Science, University of Illinois Urbana-Champaign, February 1995).
The prior art has shown that there is a need for dynamic allocation of resources. See, for example, Evaluating Management Decisions via Delegation, German Goldszmidt and Yechiam Yemeni, The Third International Symposium on Integrated Network Management, San Francisco, Calif., April 1993. An EC provides a single system image of a collection of services, typically over a collection of hosts. However, actual installations may require that services be allocated according to specific user policies, which can be dynamic. For example, a specific subset of the hosts may be allocated for secure transactions on a merchant Web server, while video on demand services is supported by another subset of hosts which include specialized hardware.
An object of this invention is to improve the overall throughput of an Encapsulated Cluster.
Another object of this invention is to reduce the aggregate delay of the remote service requests.
A further object of this invention is to provide means for a designated node to take over the operation of a failed connection-router in such a way that network clients experience no interruption of service.
In accordance with a first aspect of the present invention an Encapsulated Cluster (EC) is characterized by a Gateway node and server hosts. The gateway node (1) divides an EC into several Virtual EC (VECs), (2) dynamically distributes incoming connections within a VEC based on current server load metrics according to a configurable policy and (3) supports dynamic configuration of the cluster.
In accordance with a second aspect of the present invention a system and method are provided to enable transparent recovery from the failure of a gateway node in order to provide uninterrupted service to the clients. In accordance with the method, each node in a cluster or VEC maintains a copy of a subset of state information held at the gateway. When the gateway fails, the state information is transferred to a backup gateway.
In a preferred embodiment, the EC can appear as (1) a VEC (a single IP address for all the remote clients) or (2) as multiple VECs (aliasing several IP addresses.) The TCP-CR node owns these IP addresses and receives all their TCP connection requests. Each IP address is associated with a VEC. The TCP-CR distributes new TCP connections to hosts within each VEC according to the weights associated with the VEC. The TCP-CR supports dynamic configuration that allows: Dynamic definition of VECs. Dynamic configuration of the weights associated with a VEC. Automatic or manual management of VECs (adding or removing hosts, services, etc.). This solution allows for dynamic configuration, addition and removal of server hosts, while avoiding the problem of cached server names in the network.